The present invention relates to a power supply circuit for low-pressure discharge lamps, of the type comprising an inverter with two controlled switches which are alternately made conducting and isolating to supply a load circuit, comprising at least one lamp, with a high-frequency alternating voltage.
This type of circuit is used to supply discharge lamps of various types. Inverter power supply circuits are described, for example, in EP-A-0621743, U.S. Pat. No. 5,426,344, EP-A-0488478, U.S. Pat. No. 5,479,334, EP-A-0697803, U.S. Pat. No. 5,485,060.
At present there are various types of discharge lamp available on the market, which differ from each other in their external dimensions and in their internal characteristics, particularly in the power drawn. At present, where tubular lamps are concerned, there are, for example, two classes of lamps distinguished by their external dimensions and lamps of varying power are grouped in each category. The symbol T5 is used to identify tubular discharge lamps with a small external diameter, available with power ratings of 14 and 24 watts (lamps T5FH and T5FQ). Lamps of larger diameter are identified by the symbol T8 and are available in three different versions, namely 18, 36 and 58 watts. The ballasts or inverter power supplies available at present on the market are designed for a single type of lamp, so that there is the disadvantage of having to have a large number of inverters for the various lamps. Where compact lamps are concerned, there are different shapes and connections corresponding to different power ratings.
Furthermore, the lamps in each category are externally identical, so that there is a risk of connecting a lamp with a particular power rating in a power supply circuit designed for a different power, resulting in an incorrect power supply to the lamp.
The object of the present invention is to provide an inverter power supply which overcomes the disadvantages mentioned above.